Microcrystalline cellulose particles in photographic silver halide elements



United States Patent 3,373,023 MICRQCRYSTALLINE CELLULOSE PARTICLES IN PHOTOGRAPl-HC SILVER HALTDE ELEMENTS Vere Mafiet, East Brunswick, N..l., assigncr to E. I. du Pont de Nemours and Company, Wilmington, Del., a

corporation of Delaware No Drawing. Filed Dec. 11, 1963, Ser. No. 331,000 8 Claims. (Cl. 96-113) This invention relates to the purification of aqueous systems. More particularly, this invention relates to a method for purifying aqueous solutions or dispersions Containing water-permeable macromolecular organic col loids. The invention also relates to new photographic elements.

The presence of contaminant oils and greases in various aqueous systems creates process and quality problems. These problems are particularly apparent in coating operations wherein the surface tension of these contaminants differs from that of the material being coated. The condition described causes small areas of the final product to remain at least partially uncoated after passing through the coating operation, and these areas are known in the photographic art as repellent spots.

The invention will be described in connection with a method of removing repellency-causing contaminant oils and greases from photographic emulsions prior to coating. It should be understood that such descriptions are merely exemplary in that the invention may be adapted with little or no modification to other aqueous systems wherein similar purification problems exist.

Photographic silver halide emulsions are made by precipitating silver halides in an aqueous colloid medium. Gelatin has been used for many years as the film-forming colloid in photographic emulsions. It has been recognized, however, that because of its natural origin, the Variety and impurity of the raw material from which it is made, and the method of its preparation, gelatin will contain natural animal oils and greases. These natural oils and greases have no effect on the photochemical reaction that occurs during the exposure of the emulsion to actinic radiation, but are a cause of repellency when the gelatin emulsion is coated on a support. During the preparation of photographic gelatin or the preparation of photographic emulsions, moreover, the emulsion is occasionally unintentionally contaminated by various petroleum oils used to lubricate the apparatus involved: these oils also cause repellency.

It is known in the photographic art that the addition of various wetting agents or surface-active agents to an emulsion prior to coating will assist in providing for uniform spreading of the emulsion and will help to prevent the formation of foam bubbles and repellent spots. These agents overcome the basic problem of adequate adhesion between a hydrophobic base support and a hydrophilic emulsion. However, these agents do not remove the repellency-causing contaminants; they act to decrease the differences in surface tensions within the emulsion and, as a result, alleviate the formation of repellent spots to some extent.

The oil or grease contaminants present in the emulsion cause a different type or" repellency. In addition to repelling adherence of an emulsion to a base support, these contaminants can also cause repellency between two 3,373,023 Patented Mar. 12, 1968 emulsion layers and between antiabrasion layers and emulsion layers. The repellency defect so caused usually appears as a spot approximately circular in shape. These spots will vary widely in size, ranging from approximately a half-inch in diameter to a small point.

It is, therefore, an object of this invention to provide a simple and effective method for purifying aqueous systems. A more specific object is to provide a method of purifying aqueous colloid solutions from contaminant oils or greases. It is another object to provide a method of purification that immobilizes or removes the eifect of such contaminant oils without affecting the properties of the system. A still further object is to provide a process which is economical and can be carried out on a rela tively large scale. A still further object is to provide such a method that can be carried out efficiently and on a commercial scale. A further object is to provide a method of purification that can be used for purifying all types of aqueous photographic emulsions. Another object is to provide a method of purification that will produce an improved photographic film, i.e., a uniformly coated product that is free from bare spots. A further object is to provide new photographic elements.

The foregoing and other objects are accomplished in accordance with the elements and method of the present invention. This method for counteracting the deleterious effect of contaminant oils and greases in aqueous coating compositions containing a water-permeable, macromolecular organic colloid binding agent is characterized by bringing said solution into contact with microcrystalline cellulose particles. The microcrystalline cellulose may be introduced by adding it in particle form, stirring the mixture, and subsequently filtering out the contaminantcontaining particles, or by adding cellulose of such particle size that the particles need not be removed and can remain within the system without adverse effect, or by preparing a filter coated with the microcrystalline cellulose and subsequently passing the contaminated aqueous system through the filter.

Microcrystalline cellulose is commercially available. Some methods for obtaining microcryst'alline cellulose particles and aggregates thereof are disclosed in US. Patents 2,978,446; 3,023,104; and 3,067,037. The salient features of the methods described in those patents are as follows. Any form of purified cellulose, either native or regenerated, is acted on in a controlled acid hydrolysis. The 'acid destroys or removes amorphous portions of the original cellulose chains, the remaining unattached por tions being a particulate, nonfibrous or crystalline form as a result of the disruption of the continuity of the fine structures between crystalline and amorphous regions of the original cellulose. The crystalline aggregates are then water washed and subjected to mechanical disintegration or attrition. Mechanical disintegration of the aggregates may be carried out in several ways, e.g., by attrition in a mill, by high speed cutting action, or by the action of high pressure on the order of 5,000 or 10,000 psi. The disintegration is preferably carried out in the presence of an aqueous medium. After the mechanical disintegration, the aggregates are dried until they become a crumbly, free flowing, grainy, dry particulate material.

The aggregates of rnicrocrystalline cellulose are interspersed with pores that have a marked afiinity for natural and petroleum oils. Eac h aggregate can absorb more than its weight in oil. The ratio of weight of oil absorbed to weight of microcrystalline cellulose for the range of aggregate size, e. g., -150 microns, is of the order of 1.1/1.2 to 1. Also, the aggregates, upon being introduced into an aqueous system do not create or cause any chemical reaction, as they are inert and insoluble and, once introduced, they preferentially and selectively absorb any insoluble oils or greases present in the system.

According to one aspect of this invention, the aggregates 'are added to a gelatino-silver halide emulsion and mixed. The resulting dispersion is then filtered through a conventional paper filter of the appropriate size to remove the aggregates The aggregates have absorbed the oil present in the emulsion, and thus the oil is also removed during the filtration.

In a further aspect of this invention the aggregates to be added are of a size of 5 to 65 microns in diameter, the resulting dispersion of aggregates and gelatino-silver halide emulsion is not filtered but coated on the desired support. Because of the small particle size, the aggregates do not introduce any adverse photographic qualities and they immobilize the effect of any oily contaminants present.

In a still further aspect of this invention, the aggregates may be coated on an appropriate support such as filter paper. This filter is then used to filter the gelatino-silver halide emulsion and remove the oily contaminants from the emulsion prior to coating.

The process of this invention may be utilized with any aqueous system containing oil contaminants, and particularly photosensitive gelatino-silver halide emulsions.

The invention will now be illustrated in and by the following examples but is not limited thereto.

EXAMPLE I To an aqueous gelatin solution at 100 F. containing 5% by weight of inert bovine bone gelatin, a dye was added. The dye was used to aid in the detection of repellent spots. Part of this solution was coated and dried on an untinted', subbed polyethylene tercp hthalate (polyester) base support such as described in Alles et al. 2,627,088 and 2,779,684. The coated gelatin layer was chilled to 50 F. and dried at 85 F. and 35% relative humidity. Examination of the layer revealed infrequent small repellent spots.

To the remaining portion of the solution, ordinary petroleum lubricating oil was added while stirring the solution. The oil was added at the rate of 1% by weight of the gelatin present. Part of this solution was then coated and dried on untinted subbed polyethylene terephthalate (polyester) base support in the same manner as the original portion. Examination of the coating revealed repellent spots that were large in size and numerous in amount.

T o the remaining gelatin solution contaminated by the lubricating oil, microcrystalline cellulose (level-off D.P. cellulose) was added and stirred in for five minutes. The microcrystalline cellulose, having a range of particle sizes from to 65 microns in diameter, was added at the rate or 2.5% by weight of the gelatin present. The solution was then filtered through a conventional filter paper and subsequently coated and dried on an untinted base support in the same manner as the other portions. Examination revealed a coating that was completely free from repellent spots.

EXAMPLE II Example I was repeated except that the gelatin solution contained 5% by Weight of pigskin gelatin instead of bone gelatin. The results were the same as those described in Example I, with the coating from the solution to which the microcrystalline cellulose had been added being completely free from repellency.

EXAMPLE 111 Example I was repeated except that instead of adding lubricating oil, animal oil (cod liver oil) was added at the rate of 1% by weight of the gelatin present. The results were the same as those described in Example I.

EXAMPLE IV Example 1 was repeated except that instead of adding lubricating oil, vegetable oil (olive oil, food grade) was added at the rate of 1% by weight of the gelatin present. The results were the same as those described in Example 1.

EXAMPLE V A high speed gelatino-silver iodobromide aqueous cine emulsion containing 7.3% iodide and 92.7% bromide and 6% by Weight of gelatin was prepared and color sensitized. Part of this emulsion was coated and dried on an untinted subbed polyethylene terephthalate (polyester) base support. After the emulsion was coated, it was chilled to 50 F. and dried at F. and 35% relative humidity. Examination revealed infrequent small repellent spots.

To the remaining portion of the emulsion, silicone oil, i.e., Dow Corning 35-B silicone emulsion to which ethyl alcohol had been added to separate the oil, was added at the rate of 1% by weight of the gelatin present. Part of this emulsion was then coated and dried on an untinted subbed polyester base support in the same manner as the original portion. Examination revealed many repellent spots ranging in size from small to large.

To the remaining emulsion contaminated by the silicone oil, microcrystalline cellulose was added at the rate of 2.5% by weight of the gelatin present and stirred for a few minutes. The emulsion was then filtered through a conventional filter paper and subsequently coated and dried on an untinted subbed polyester base support in the same manner as the other portions. Examination reveiled a coating completely free from repellent spots.

The original emulsion and the emulsion that had been contaminated and subsequently purified were exposed simultaneously in a Type 1B sensitometer and developed for 6 /2 minutes at 68 F. in a developer of the following composition:

These results indicate that the process of the invention does not have any adverse effect on a sensitized photographic emulsion.

EXAMPLE VI To an aqueous gelatin solution at F. containing 5% by weight of inert bovine bone gelatin, a dye was added. Part of this solution was coated and dried on an untinted subbed polyester base support, the coating being chilled to 50 F. and dried at 85 F. and 35% relative humidity. Later examination revealed infrequent small repellent spots.

To the remaining portion of the solution ordinary lubricating oil was added at the rate of 1% by weight of the gelatin present. Part of this solution was coated and dried on an untinted subbed polyester base support in the same manner as the original portion and subsequent examination revealed many repellent spots of various sizes.

The remaining gelatin solution contaminated by the lubricating oil was filtered through a conventional filter paper, the upper side of which had previously been coated with a layer of microcrystalline cellulose 0.01 inch thick. The solution was then coated and dried in the same manner as the prior portions, and subsequent examination revealed a coating completely free from repellent spots.

To coat the filter paper, a 25% slurry of 'microcrystalline cellulose in distilled water was poured onto filter paper supported on a mesh. The thickness of the layer was made .008 inch, .010 inch and .012 inch on various samples. All were equally effective when used as described above.

EXAMPLE VII To an aqueous gelatin solution at 100 F. containing 5% by weight of gelatin, lubricating oil was added at the rate of 1% by weight of the gelatin present. The solution was divided and microcrystalline cellulose was added in the amounts shown in the following table.

Percent of microcrystalline cellulose by weight of The samples, without filtration, were coated onto an untinted subbed polyester base support. In all samples except Number 1, the repellency causing effect of the lubricating oil was removed.

Further, the addition of the solid particles of microcrystalline cellulose imparted a matte surface to the coatings as measured by the acceptability of a No. 2 pencil mark. The degree of matting ranged from nil on Sample 1 to light, moderate, heavy, and very heavy on Samples 2 through 5, respectively. This result leads to the conclusion that microcrystalline cellulose may also be used to provide a matte surface in products where such a surface is desired.

EXAMPLE VIII With an aqueous subbing solution composed of a vinylidene chloride/methacrylate/itaconic acid copolymer, such as described in Swindells US. Patent 2,698,235, the procedures set forth in Example I were repeated. The subbing solution was processed under the same conditions as the gelatin solution and the results were the same as those described in Example I.

While the foregoing examples are concerned with aqueous gelatin solutions and, more particularly, aqueous gelatino-silver halide emulsions, the invention is not limited to this particular water-permeable organic colloid. Aqueous solutions of other such macromolecular colloids of synthetic or natural origin can be similarly beneficiated or improved. Thus, aqueous solutions of casein, albumin, interpolyamides, agar-agar, polyvinyl alcohol, polyacrylamides and polyvinylacetals may be used. In addition, certain other polymers or polymer mixtures such as polyvinyl-N-vinyllactams, butadiene-acrylonitrile copolymers, vinyl acetate-vinyl-stearate copolymers, styrene-butadiene copolymers, alkyd and acrylic resins may be used in combination With gelatin.

Aqueous gelatino-silver halide emulsions containing polymeric materials which enhance covering power, e.g., dextran, dextrin and polyvinyl pyrrolidone, can be treated in a similar manner to remove contaminant oils and greases.

The process of the invention can be used with any aqueous colloid system containing contaminant oils, and is particularly useful in aqueous photographic systems.

The invention can be used with all aqueous gelatin solutions used to form gelatin sub-layers, gelatin filter layers, antihalation layers which contain dyes and pigments that absorb preselected wave lengths of light, and antiabrasion layers. The invention is useful with aqueous dispersions of water-permeable organic colloids containing particulate matter, including silver halide grains, magnetizable materials or phosphors in suitable aqueous mediums such as water, aqueous ethanol, etc. It is useful with resin substratum or subs, such as an aqueous dispersion of a vinylidene chloride/methacrylate/itaconic acid copolymer of the type described in Swindells US. Patent 2,698,235. The invention can be used with any gelatinosilver halide emulsion, such as silver iodobromide, silver bromochloride, or silver bromide. The invention is useful not only with black and white photographic and x-ray emulsions, but also with emulsions for stripping films for silk screen and gravure processes and photographic emul sions used in color photography. The invention is useful with emulsions that contain color formers, such as those disclosed in Dorough US. 2,380,032; Dorough US. 2,380,033; and Woodward and Chu US. 2,927,024. It is also useful with emulsions containing any of the wellknown optical sensitizing dyes as well as non-optical sensitizers such as sulfur sensitizers containing labile sulfur, e.g., allyl isothiocyanate, allyl diethyl thiourea, phenyl isothiocyanate and sodium thiosulfate, the polyoxyalkylene ethers in Blake et al., US. 2,400,532, and the polyglycols disclosed in Blake et al., U.S. 2,432,549. Also, the invention is useful with emulsions containing other nonoptical sensitizers such as amides, Staud et al., U.S. 1,925,508, and metal salts, Baldsiefen, US. 2,540,085. The emulsion can also contain conventional antifoggants, e.g., benzotriazole and triazaindenes; the usual hardeners, i.e., chrome alum, formaldehyde, etc.; and other adjuvants such as matting agents, plasticizers, toners, optical brightening agents, etc.

The process of the invention has many advantages, the principal one being the fact that it effectively removes from various aqueous systems repellency-causing contaminants without adversely affecting the systems. It greatly reduces the yield losses in various coating operations wherein these contaminants cause problems, particularly in the photographic industry where the repellency of coated stock is a problem of long standing. A further advantage is that a filter medium impregnated with the microcrystalline cellulose as previously described can be adapted within the framework of many present in-line filter operations.

I claim:

1. A photographic element having a water-permeable organic colloid layer containing microcrystalline cellulose particles said element having a water-permeable organic colloid layer containing light-sensitive silver halide.

2. A photographic element having a gelatino-silver halide emulsion layer containing microcrystalline cellulose particles.

3. A photographic element having an outer matte layer comprising a water-permeable organic colloid having dispersed therethrough microcrystalline cellulose particles and an inner contiguous water-permeable organic colloidsilver halide emulsion layer.

4. A method for counteracting the deleterious effect of contaminant oil and greases in aqueous coating compositions containing a water-permeable, macromolecular organic colloid binding agent having dispersed therethrough light-sensitive silver halide grains characterized by bringing said solution into contact with microcrystalline cellulose particles.

5. A method according to claim 1 wherein said particles are level-off D.P. cellulose particles.

6. A method according to claim 1 wherein the cellulose particles embody aggregates of sizes from 5 to microns in average diameter.

7. A method according to claim 1 wherein the particles are filtered from the aqueous coating composition.

7 8 8. A method according to claim 1 wherein said colloid OTHER REFERENCES is gelatln- Crawford, B. 1-1., Small-Scale Preparation of Fine- Reierences Cited Grain (Colloidal) Photographic Emulsions. National Physical Laboratory Noles on Applied Science, N0. 20, UNITED STATES PATENTS 5 London, Her Majestys Stationery .Office, 1960, pp. 67.

3,169,870 2/1965 Knox et a1. 96-94 3,179,587 4/1965 Battista et J. TRAVIS BROWN, Acting Primary Examiner.

O G PATENTS NORMAN G. TORC-HIN, Examiner. 510,090 9/1939 Great Britain, 10 C. E. DAVIS, Assistant Examiner. 

4. A METHOD FOR COUNTERACTING THE DELETERIOUS EFFECT OF CONTAMINANT OIL AND GREASES IN AQUEOUS COATING COMPOSITIONS CONTAINING A WATER-PERMEABLE, MACROMOLECULAR ORGANIC COLLOID BINDING AGENT HAVING DISPERSED THERETHROUGH LIGHT-SENSITIVE SILVER HALIDE GRAINS CHARACTERIZED BY BRINGING SAID SOLUTION INTO CONTACT WITH MICROCRYSTALLINE CELLULOSE PARTICLES. 